Orbital Mechanics Questions

[Brad Hindman]

I am not sure if a star of the mass of Jupiter can maintain the fusion process neccessary for a "real" sun. (And it would probably be artificially or "accidently" initiated)
But my main problem is the additional source of heat/radiation/light. I am not sure if it wouldn´t screw with the ecosystem of a planet.
(I think the scenario of 2010 would be fatal for humanity and most earth life - If the ecosystem of the planet was created with the two suns, this doesn`t apply...)

Since, Jupiter isn't large enough to be a star in its own right, we can't really say anything about its energy output in this scenario without knowing how the planet was artificially fulminated. Not only is some outside agency required to initiate fusion in the gas giant, but something is required to keep it burning. The energy output is completely dependent on what that something is and how it works. So ... the GM has a pretty free hand in this case.

 

[Lord Satan]

Planetary Science

If it helps I study planetary science and if there was a hard sci-fi setting then in reality Jupiter would not be able to become a star, it needs 13 times more mass, and even then would become a Brown Dwarf as the Deutrinium inside starts to go through a fusion reaction from core pressure... however, taking that aside there are some other problems, at this time of writing Jupier has 40 satelites including four Galilean satelites, Io, Europa, Ganymede and Callisto (the 4 satellites large enough to be geologically planets in their own right), unfortunately Jupiters gravity is intense enough that each of these moon's are tidally locked with Jupier and so always have one side permanenetly facing jupiter with the other side permanenetly facing away, so, if Jupiter became a star, one side would be permemenetly scorced (as they are far too close anyway) while the other side would be shielded from the heat but have their atmosphere, if any, blown off by the now high powered solar winds of a virtually adjacent star... then their is the radiation, as it stands, Io has over one metric ton of it';s material stripped by Jupiter by Jupiters magnetic field as it passes that close to Jupiter (the tidal gravity of jupiter is what causes it's ridiculous level of volcanic activity) if Jupiter became a star most life would be killed long before reaching the moon's by incredible levels of radiation that no current technology can dampen let alone block and that's not even going on to whether the moon would be habitable (the far side at that since the near side would be hotter than the surface of a Jupiter-star due to corona radiation. Other planets would have a temperature increase but they would not have differentiated orbits as Jupiters mass affects orbital periods and this should not change but the disturbance of nearby smaller satellite to jupiter would cause some of the "smaller" ones to be thrown out from Jupiter through the void of the solar system causing untold damage on any planets hit (small by these standards would be Extinction Level Event asteroids), so, really, you may have issues...

 

[Lord Satan]

...just as a quick note, if your going Sci-fi, you could have a hypothetical advanced civilisation "push" Europa out of orbit to a much more distant orbit from Jupiter by the old fashioned method of multiple small fusion rockets since one side faces jupiter, this would have the dual benefit of making it easier to push out before stabilisjg it without having to rotate rockets and also means you can impart spin later... it also means when you use a presumably artifical means of igniting jupiter then Europa will be far enough to be habitable, it's ice will melt into oceans and it already has free oxygen trapped in the ice from previous eaons of photodissociation... it should be noted that even today, Jupiter actually radiates more heat than it recieves from the sun so as another alternative a VERY close moon could actually be heated enough from present day jupiter if it had a thick atmosphere of carbon-dioxide, oxygen and ozone (to protect against extreme radiation).

 

[Mr. Draco]

Actually, iirc, it would be a bad idea to have moons close enough to jupiter (in its present state) to be warmed significantly by Jupiter's radiative output. Each planet has a so-called "Roche Limit," which is basically the closest a moon can exist without being torn apart by the gravity differential between the portion of it nearer to the planet and that further away.

Another way of saying it, is that since gravity is stronger the closer you are to the planet, the gravitational pull on the near side of a moon will be greater than that on the far side, thus producing a "stretching" action. The closer the moon comes, the greater the stretching force, and eventually, when the moon passes within the roche limit, the moon is torn apart. That's how all of the rings around the gas giants formed. So if one of Jupiter's moons was close enough to be heated significantly by jupiter, then it'd almost certainly be within the roche limit, and thusly torn apart and added to Jupiter's rings.

 

[Aesmael]

First, by what you've said so far, sounds like having the jovians where/as they are and habitable is part of the campaign. You don't want help turning Jupiter into a realistic life source, right?

So: The moons will always have the same face pointed Lucifer's way unless people have expended effort to make them rotate. This will not necessarily make them uninhabitable - there was a recent paper which found that planets orbiting stars in this manner would not end 'fire and ice' (hearsay from me, I have not been able to track it down to read yet).
Unless you take Lord Satan's suggestion (I'm tempted to recommend it, just so I can say I did) and move them out from their current positions the years will be very short. The current range is from 1.7 days for Io to ~16 for Callisto. Not necessary to move them though, if you are just handwaving the illumination, but remember that Lucifer will not be as bright. Unless you want to go into math just say it is bright (that's in regards to Mars and Terra, I assume you know how you want it to look from them)

Consider that most of the jovian moons are in resonant orbits with each other. Europa, for example, is in the same position in Io's sky every two (Io) orbits. You might want to play up the regularity of their skies if you go for that.

Is this intended to be an adaption of our solar system, or just a similar setup to the Odyssey stories you mentioned? (curiosity)

Pbartender, although those planets seem to be very common, it is unlikely they would have habitable moons. Satellites tend to get stripped off them when they orbit that close. Which does not mean you can't set it up that way, but it would probably be a temporary situation and any inhabitants more likely arrived from elsewhere than evolving on site.

Interesting book, will check it out. Had considered writing something similar, but not yet qualified.

Lord Satan, student or?

 

[Aesmael]

Actually, iirc, it would be a bad idea to have moons close enough to jupiter (in its present state) to be warmed significantly by Jupiter's radiative output. Each planet has a so-called "Roche Limit," which is basically the closest a moon can exist without being torn apart by the gravity differential between the portion of it nearer to the planet and that further away.

Another way of saying it, is that since gravity is stronger the closer you are to the planet, the gravitational pull on the near side of a moon will be greater than that on the far side, thus producing a "stretching" action. The closer the moon comes, the greater the stretching force, and eventually, when the moon passes within the roche limit, the moon is torn apart. That's how all of the rings around the gas giants formed. So if one of Jupiter's moons was close enough to be heated significantly by jupiter, then it'd almost certainly be within the roche limit, and thusly torn apart and added to Jupiter's rings.

Best to make it a very small one, then.

 

[Achan hiArusa]

Jupiter as a Sun

To become a L class brown dwarf (capable of Deuterium Fusion) it would have to to 13 Jovian masses (0.013 Solar Masses). To have the same gravitational effect as Jupiter it would have to be about 3.5 times as far away as it is now (18.2 AU or just inside Uranus's orbit). It would be dimmer than Jupiter due to its size (which would increase it) and distance (which would decrease it). It will be a T class brown dwarf at about 28 Jovian masses (0.028 Solar Masses) it would have to be 4.5 times as far away (24.8 AU or just inside Neptune's orbit), it would glow slightly red on the order of 10,000,000 years and would then cool down. At about 50 jovian masses (0.050 Solar Masses) it would be a true star (M class, red colored) and would have to be 5.5 times as far away (28.6 AU or still just inside Neptune's Orbit). As for Day/Night Cycles I would find a night sky simulator (Carinasoft.com has a trial version of Voyager III) and then just track Uranus or Neptune in the night sky. If you want to borrow a real universe system look at the Extrasolar Planets encyclopedia (www.obspm.fr/encycl/encycl.html) or Extrasolar visions (www.extrasolar.net). The first one is more technically accurate, the second has pretty pictures and diagrams.

 

[Pbartender]

Pbartender, although those planets seem to be very common, it is unlikely they would have habitable moons. Satellites tend to get stripped off them when they orbit that close. Which does not mean you can't set it up that way, but it would probably be a temporary situation and any inhabitants more likely arrived from elsewhere than evolving on site.

Oh, certainly, I know that... My point was that having multiple habitable planets around close orbiting planets is still a (slightly) better and more likely explaination, than a 'Lucifer-Sun' type binary system. And there is enough basis in real science that it is at least remotely feasible (in a science-fiction sort of way) to most people who aren't astronomers or are willing suspend a small modicum of disbelief.

Besides, such a system (especially if there was native life) would be unusual enough to provoke questions as to how it had formed... What an excellent basis for a campaign, eh?

Or what if all those terraformed artificial planetary environments were slowly starting to degrade? Now the PCs must find a way to reverse it, or find another starsystem with a stable habitable planet to relocate to.

 

[Achan hiArusa]

System Stability

Just got confirmation from my master's advisor Dr. Lacy, the minimum stable distance in a G-M system would be 10 AU, but there would be no planets between a 1 AU earth-like planet and the star. The star has to be 10 times as far away as any planet in order to have a dynamically stable system, so to have a Mars-like planet the second star would have to be 16 AU out. Here is our system for comparison:

Mercury Venus Earth Mars Asteroids Jupiter Saturn Uranus Neptune Pluto
0.4 0.7 1.0 1.6 2.8 5.2 10.0 19.6 30.0 39.4

So you could put a star in Saturn's orbit and it would be stable and it could have terrestrial planets out to the same distance. Any gas giants would have to be very far away from the system.

 

[Aesmael]

Oh, certainly, I know that... My point was that having multiple habitable planets around close orbiting planets is still a (slightly) better and more likely explaination, than a 'Lucifer-Sun' type binary system. And there is enough basis in real science that it is at least remotely feasible (in a science-fiction sort of way) to most people who aren't astronomers or are willing suspend a small modicum of disbelief.

Besides, such a system (especially if there was native life) would be unusual enough to provoke questions as to how it had formed... What an excellent basis for a campaign, eh?

Or what if all those terraformed artificial planetary environments were slowly starting to degrade? Now the PCs must find a way to reverse it, or find another starsystem with a stable habitable planet to relocate to.

True. And it doesn't stop me from using them, but it sounds like ajanders already has a mystery planned for the system.

Forgot to mention earlier, an atmosphere on jovian moon sized objects (our moon) would probably be a temporary thing (well, a million-year plus temporary thing, but still a temporary thing), if you care to include it. Not sure exactly how long it would last, but I have a lecture in a couple of hours that might cover the topic. Seems like something else you can handwave though.

Actually, just reread the first post and it seems we may have gone overboard in our help. A sky simulator would definately help. Does Voyager III allow you to make your own modifications? I know Starry Night does (hours of fun!), but I think you have to pay for that. Remember that Lucifer must be dimmer than Sun if you want things to stay where they are.